Apparatus for cooling pellets severed from extruded plastic strands

ABSTRACT

PELLETIZING APPARATUS INCLUDING A BARREL WITH A MIXER SHAFT THEREIN, A DIE WITH AXIALLY EXTENDING PORTS FOR EXTRUDING STRANDS OF PLASTIC OR OTHER EXTRUDABLE MATERIL THERETHROUGH, A ROTARY KNIFE ASSEMBLY WHICH CUTS THE STRANDS INTO PELLETS, AND A ROATING PELLET COLLECTING HOUSING TO WHICH LIQUID IS SUPPLIED IN A MANNER TO FORM A CENTRIFUGALLY MAINTAINED PELLET COLLECTING COOLANT ANNULUS MOVING AS A STREAM IN A SPIRAL PATH AWAY FROM THE DIE.

R. W. MILER APPARATUS FOR COOLING PELLETS SEVERED FROM EXTRUDED PLASTICSTRANDS Filed July 10, 1968 Sept. 2s, 1.911

United States Patent 3,608,142 APPARATUS FOR COOLING PELLETS SEVEREDFROM EXTRUDED PLASTIC STRANDS Richard W. Miler, Saginaw, Mich., assignorto Baker Perkins Inc., Saginaw, Mich. Filed July 10, 1968, Ser. No.743,783 Int. Cl. B29f 3/00 U.Sk Cl. 18-12 7 Claims ABSTRACT OF THEDISCLOSURE Pelletizing apparatus including a barrel with a mixer shafttherein, a die with axially extending ports for extruding strands ofplastic or other extrudable material therethrough, a rotary knifeassembly which cuts the strands into pellets, and a rotating pelletcollecting housing to which liquid is supplied in a manner to form acentrifugally maintained pellet collecting coolant annulus moving as astream iu a spiral path away from the die.

One of the prime objects of the invention is to provide an improvedapparatus for cooling pellets which are man- Vfactured in apparatusdescribed in the instant assignees copending application Ser. No.688,398, filed Dec. 6, 1967, and entitled Apparatus for ExtrudingStrands and Cutting Them Up Into Pellets.

A further object of the invention is to provide an apparatus of thecharacter described wherein centrifugal forces are utilized to keep thepellets immersed in a stream of water which moves in a generally axialdirection away from the extruding die and toward a discharge housing.

Another object of the invention is to provide cooling apparatus forcooling wherein the pellets are moved in a generally spiral path in thepellet trapping housing rather than directly down the length thereof,and thus remain in the coolant stream for a greater length of time.

Another object of the invention is to design cooling apparatus forcooling which may be used with all types of plastic materials includingpolypropylene, without utilizing water or another coolant at the dieface as in the conventional in-line underwater cutter.

Still another object of the invention is to provide a highly reliableand less expensive pelleting and pellet cooling system which requiresless floor space than conventional systems and does not require that abearing housing be in a zone of high heat or attached directly to theextruder barrel.

Other objects and advantages of the invention will be pointed outspecifically or will become apparent from the following description whenit is considered in conjunction with the appended claims and theaccompanying drawings, in which:

FIG. 1 is a sectional, side elevational view of the apparatus.

FIG. 2 is an enlarged fragmentary, transverse sectional view taken onthe line 2-2 of FIG. 1.

Referring now particularly to the accompanying drawings in which I haveshown a preferred embodiment of the invention only, a letter B generallyrefers to a jacketed, tubular mixing barrel which may include annularpassages 11a and 11b for circulating a temperature maintaining heatingor cooling fluid, depending on the mixing operation to be performed. Amixer of this general character is disclosed in the aforementionedapplication and in the present assignees U.S. Pat. No. 3,023,455,granted Mar. 6, 1962 to Herbert F. Geier and Henry F. Irving, and thepresent machine similarly includes a feed hopper leading into thechamber or bore 11 of the barrel B fice for delivering the ingredientsto be mixed to the chamber 11. Normally the plastic material to bepelletized will be fed to the hopper 10 in the form of plastic beads andwill be heated in the barrel 11 to its melting temperature.

Provided in the barrel B are circumferentially spaced radially inwardlyprojecting teeth or lugs 12 of the character disclosed in the patentmentioned, which cooperate with interrupted helical threads or blades 13provided on a portion 14 of a mixer shaft generally designated S inhelical formation in a manner to achieve the intimate blending andkneading of the material introduced to the chamber 11 through hopper 10.The threads or flight sections 13 are so pitched that if the shaft S isrevolved in a clockwise direction as viewed from the right end of themachine (see the arrow a), the material will be moved forwardly fromright to left, it being understood that shaft S is simultaneouslyreciprocated in timed relation with its rotation and the disposition ofteeth 12 so that during the stroke of the shaft S, the teeth 12 passthrough the spaces b between the interrupted blades 13. It may beassumed that the blades which form the thread portions 13 areinterrupted at degree intervals, and the shaft then, of course, mustrotate 180 degrees during both the forward and rearward portions of thereciprocatory stroke. Provided to drive the shaft S in a rotary andreciprocating stroke is a motor and cam assembly generally designated 15of the same type shown in the aforementioned patent and patentapplication and in view of this, it is deemed unnecessary to present aspecific disclosure thereof here- 1n.

At its front end, the shaft portion 14 mounts an advancing screw section24, also forming part of shaft S, and having flights 25 which move theplasticized material forwardly in the same manner as do the flights 13.It will be observed that section 24 has a bore 24a within which the endof shaft portion 14 is received. Mounted on the front end of theadvancing screw section 24 is an extruding head assembly generallydesignated 26, also forming part of the shaft S, and reciprocating andrevolving therewith which includes a sleeve member 27 having a reducedend portion 27a, received in a recess 25a in the front end of the screwsection 24 and secured by a bolt 27b which extends into the shaftsection 14.

The assembly 26 includes a pair of die plates 28 and 29 which cooperateto discharge the material in the form of strands and are provided withcommunicating, circumferentially spaced material expressing passages 28aand 29a respectively. It will be observed that the plate 29 has arearwardly extending sleeve extension 30 which is spaced from the sleeve27 to provide an annular passage 31 leading to the extruding orificesformed by openings 28a and 29a. The rear portion of the sleeve extension30 is beveled as at 30a to direct the plasticized material inwardly tothe chamber 31. Bolts 32 may be provided to secure the plate 29 to thesleeve 27 and bolts 33 may be provided to secure the plate 28 to theplate 29. Because the chamber 31 reciprocates With the screw section 24and shaft section 14, material is expressed through the exit orifices28a in a steady stream rather than in a pulsating stream.

Mounted forwardly of the extruding head 26 which extrudes the strands ofplastic material, is a strand cutting and pellet cooling assemblygenerally designated 34, which includes an outer surrounding cylindricalhousing 35 having an end opening 37 which permits reciprocation androtation of extruding head 26 therein, The housing 35 is rotatablysupported by bearings 38 mounted by bearing supports 39 on a supportbase 40 and its forward end is rotatably received within a bore 41provided in a stationary discharge housing 42. It will be seen that base40 also mounts a bearing support 43 for the front end of an elongated,cutting knife carrying, tubular shaft 44- which is supported at itsopposite end by the extruding assembly 26, the shaft 44 extending freelythrough an opening 4S provided in the one Wall of the discharge housingor chute 42 as shown. The bearing 43a supports the shaft 44 for rotationand reciprocation and a return spring 46 is provided between a flange44a on the shaft 44 and axially iixed bearing 43 as shown.

It will be observed that the shaft 44 is interior-ly partitioned as at44h and rotatably mounts a center member 47 journaled in a bearingsleeve 48. The one end of the center member 47 is tapered as at 47a androtatably received in a center opening 28h provided centrally in the dieplate 28. Mounted on the shaft 44 for rotary movement therewith andsliding movement thereon is a cuta knife holding sleeve 50 with a key 51received in an elongated slot 52 which permits axial movement of theknife assembly 49. The cutting knives 53, which are carried by thesleeve 50, are revolved past the orifices 28a in a direction counter tothe rotation of shaft S as in the aforementioned application and may beof exactly the construction described in that application. The shaft 44may be driven by a belt 53 in a direction c counter t0 the direction ofrevolution of shaft S via a sheave 54 and reciprocates with shaft S. Theknife holder sleeve 50 is, as noted mounted for axial movement on theshaft 44 if it should be necessary such as when a foreign body jamsbetween the knife blades 53 and the die face of the plate 28, coilspring 55 being provided, however, to normally bear against the sleeve50 and maintain the cutting edges of the knife blades 53 in engagementwith the face of die plate 28.

Provided forwardly of the cutting knife assembly 49 is a radiallyangularly disposed deflector or 'baffle plate S6 for directing asuitable coolant iluid such as water, centrifugally expressed throughcircumferentially spaced ports 57 provided in the shaft 44. The bailledisk 56 also functions as a fixed base or spring support for spring 55.Provided to revolve the pellet collecting housing 35 counter to thedirection of rotation a of shaft S are belts S8 which drive thecylindrical housing 35 via a sheave 59 ata speed which developsconsiderable centrifugal forces.

In operation plastic material to be pelletized is supplied to the mixerchamber 11 through the hopper 10 in any suitable manner, but usually inparticulate form and then is melted within the chamber 11 andcontinuously mixed and kneaded therein. Typical plastics which may beprocessed are polyethylene, polyvinylchloride, polystyrene, polyurethaneand polypropylene, but many plastics and other materials may also besuitably processed by the apparatus. The chamber 11 will be maintainedat the extruding temperature of the material by circulating a heatingmedium through the jacket chambers 11a and 11b and the plastic materialwill be forwarded continuously by the flights 13 and advancing screwportion 24 to the chamber 31 and out the aligned orifices 29a and 28a inthe form of continuous strands.

The knife blades 53, which are rotated at a high rate of speed in thedirection c, counter to the direction of rotation a of the shaft S anddie plates 28 and 29, hurl the plastic pellets through the coolant fluidcurtain formed by the expressing orices 57 in shaft 44 and the bailledeflector plate 56 to the interior surface of the rotating pelletcollecting housing 35. Coolant fluid, being fed in through the shaft 44continuously in the direction of the arrows a', is centrifugallyexpressed outwardly through ports 57 and is deflected by the annularbaflie 56 to form the radially and forwardly inclined curtain e whichthen is centrifugally maintained as a moving stream f of some depth onthe interior of the rotating housing 35. Thus, because of the speed ofrotation of housing 35, a tubular annulus of a suitable coolant such aswater is formed at the interior wall of the housing 35 and movesforwardly in a spirally flowing stream which may make several completerevolutions before reaching the discharge housing 42. The centrifugalforce involved is sufficient not only to maintain the hollow annulus ofcoolant but also to maintain the heavier pellets in submerged conditionwithin the forwardly moving annulus stream. Because the pellets p passimmediately through the fluid curtain e and are immersed in the streamthey are cooled suiciently to prevent their agglomeration in the housing35 and after they are discharged to the housing 42.

The shaft 44 rotates in the opposite direction c, While reciprocatingwith the extruding head assembly 26, as does the knife assembly 49. Withthe direction of rotation of the knife assembly 49 opposite to therotation of the extrusion head assembly 26 a proper trajectory for thepellets p cut off is achieved which passes them in the path shown inFIG. l. The spring 46 is compressed, when the knife assembly 49 andshaft 44 are moved forwardly from right to left in FIG. l with theextruding head 26 and shaft S, and operates to return the shaft 44 whenthe shaft S returns in the left to right direction in FIG. l. Becausethe baie 56 directs the coolant curtain e in a forward as well as aradial direction, the coolant is prevented from reaching the die plate28 and affecting the necessarily uniform temperatures which must bemaintained at the expressing orifices 28a and 29a.

It is to be understood that the drawings and descriptive matter are inall cases to be interpreted as merely illustrative of the principles ofthe invention rather than as limiting the same in any way since it iscontemplated that various changes may be made in the various elements toachieve like results without departing from the spirit of the inventionor the scope of the appended claims.

I claim:

1. In an extruder: barrel means having a chamber; means forl supplyingmaterial to be extruded to said chamber; shaft means in said chamberwith material advancing means thereon for advancing material toward oneend of said chamber; die means having generally axial extrusion ports atsaid end of the chamber through which said material is extruded; rotaryknife means adjacent said ports for cutting the material extrudedtherethrough into pellets; pellet collecting housing means in generallysurrounding relation with said knife means and receiving pellets hurledoutwardly therefrom as they are cut; means for suppplying a liquidcoolant to said pellet housing means; and means for rotating said pellethousing and causing the liquid coolant to form an axially proceedingstream on the interior wall of said pellet housing in which the pelletsare received and transported.

2. The combination defined in claim 1 in which said liquid coolant isdelivered to the end of the pellet housing adjacent said knife means andmeans is provided for directing it peripherally to said pellet housingand away from said die means to cause it to iiow in a direction awayfrom said die means.

3. The combination deiined in claim 2 in which said directing meanscomprises directing means disposed between said knife means and coolantdelivery means and causing said coolant to form a generally radialcurtain through which the pellets are hurled by said knife means.

4. The combination deiined in claim 3 in which coolant delivery meansfor the machine comprises a rotatably supported tubular shaft mountingsaid knife means and directing means and having a series ofcircumferential ports, adjacent the directing means and on the side ofsaid directing means remote from the knife means, through which thecoolant is expressed; and means drives said tubular shaft.

5. The combination defined in claim 3 in which said directing meanscomprises disk-shaped deiiector means extending radially at an angleaway from said knife means.

6. The combination defined in claim 4 in which said die means has ncenter opening and said tubular shaft has a center received therein.

7. In an extruder: barrel means having a chamber; means for supplyingmaterial to be extruded to said chamber and advancing it toward one endof said chamber; References Cited die means having extrusion ports atsaid end of the chamber through which said material is extruded; knifemeans, UNITED STATES PATENTS as they are cut; means for supplying acoolant to said pellet housing means; and means for revolving saidpellet H' A' KILBY JR" Prmary Exammer housing collecting means andcollecting said coolant at 10 U.S. C1. X.R. the inner periphery thereof.18-1

